I've noticed this too. I can only react or upvote/downvote sometimes, and that goes with not being able to see who downvoted or upvoted posts as well. I hope this can be fixed soon.
Issue with reactions & up/down votes (its fixed now, thank you!)

Maybe two weeks ago, I noticed all of the past reactions to all posts/comments had disappeared for me. I have a screenshot from the Dead at Night Thread from Off Topic. it has no up/down votes or reactions. I believe before this broke, it had over a hundred of them.
I also noticed what I leave only stays for a little while. I reacted to someone's post yesterday, and when I looked back in the thread a little while later, it was gone.
Have you tried clearing your browser cache?

Maybe two weeks ago, I noticed all of the past reactions to all posts/comments had disappeared for me. I have a screenshot from the Dead at Night Thread from Off Topic. it has no up/down votes or reactions. I believe before this broke, it had over a hundred of them.
I also noticed what I leave only stays for a little while. I reacted to someone's post yesterday, and when I looked back in the thread a little while later, it was gone.
Have you tried clearing your browser cache?
Not yet, I'll try it in a bit and tell you if it fixes it or not. Thanks!

Maybe two weeks ago, I noticed all of the past reactions to all posts/comments had disappeared for me. I have a screenshot from the Dead at Night Thread from Off Topic. it has no up/down votes or reactions. I believe before this broke, it had over a hundred of them.
I also noticed what I leave only stays for a little while. I reacted to someone's post yesterday, and when I looked back in the thread a little while later, it was gone.
Have you tried clearing your browser cache?
Not yet, I'll try it in a bit and tell you if it fixes it or not. Thanks!
I cleared my cache and cookies and it worked, thank you!

History> delete browsing data (left side of the screen)> cookies and other site data, cached images and files> delete data
Maybe two weeks ago, I noticed all of the past reactions to all posts/comments had disappeared for me. I have a screenshot from the Dead at Night Thread from Off Topic. it has no up/down votes or reactions. I believe before this broke, it had over a hundred of them.